Types of PrecipitationTypes of Precipitation Precipitation comes in two formsPrecipitation comes in two forms

Liquid – rain, drizzleLiquid – rain, drizzle Solid - Solid - freezing rain or drizzlefreezing rain or drizzle

snowsnow sleet or ice pelletssleet or ice pellets snow pellets or graupelsnow pellets or graupel snow grainssnow grains hailhail

The vertical temperature structure of the The vertical temperature structure of the atmosphere determines whether liquid or solid atmosphere determines whether liquid or solid precipitation will fall.precipitation will fall.

RainRain

►Liquid drops with a diameter of 0.5 Liquid drops with a diameter of 0.5 mm or moremm or more

►Most rain begins as snow high in the Most rain begins as snow high in the atmosphere that melts in the warmer atmosphere that melts in the warmer air of the lower atmosphere to fall as air of the lower atmosphere to fall as rain.rain.

Rain IntensityRain Intensity

Very Light: widely spaced drops do not widely spaced drops do not completely wet groundcompletely wet ground

Light: produces trace to 0.10 inches/hour: produces trace to 0.10 inches/hour

Moderate: produces 0.11 – 0.30 : produces 0.11 – 0.30 inches/hourinches/hour

Heavy: produces over 0.30 inches/hour: produces over 0.30 inches/hour

DrizzleDrizzle

►precipitation in the form of liquid drops precipitation in the form of liquid drops with diameters less than 0.5 mmwith diameters less than 0.5 mm

►reduces visibility more than light rain reduces visibility more than light rain because there are many more drops in because there are many more drops in a shower of drizzle than in a shower of a shower of drizzle than in a shower of light rainlight rain

Drizzle and RainDrizzle and Rain

Heavy Drizzle vs. Heavy RainHeavy Drizzle vs. Heavy Rain

QuestionQuestion

►How are amounts of rain classified?How are amounts of rain classified? A. visibility limitsA. visibility limits B. inches per hourB. inches per hour C. centimeters per hourC. centimeters per hour

Freezing Rain or Freezing Freezing Rain or Freezing DrizzleDrizzle

liquid drops that fall into a layer liquid drops that fall into a layer of below freezing air close to the of below freezing air close to the ground and freeze on contactground and freeze on contact

glaze surfaces with a coating of glaze surfaces with a coating of iceice

Freezing Rain

Why is freezing rain so dangerous?

SNOW

solid white or translucent ice crystals mainly branching in hexagonal forms

most precipitation forms as snow

Snowfall Intensity

Very Light: Scattered flakes do not completely wet or cover the ground

Light: visibility is 5/8 of a mile or more

Moderate: visibility is less than 5/8 mile but not less than 5/16 of a mile

Heavy: visibility is less than 5/16 of a mile

Snow

Lots of snow

• Snow Storm Time Lapse

Heavy snow

Sleet or Ice PelletSleet or Ice Pellet

• sleet consists of transparent or translucent pellets of ice less than 5mm in diameter

• usually sleet is spherical

• formed when snow falls through above freezing and then below freezing layers of air

• pellets bounce off of surfaces on contact

Sleet

Snow Pellets or Graupel

white, opaque, nearly round ice particles similar to snow in structure

formed when ice crystal falls through layers of water droplets that stick together to make it larger

ranges in size from 2 to 5 mm in diameter often falls in a shower before or with snow

when surface temperatures are very near freezing

Small Graupel

Graupel

Snow Grains

very small, white, opaque particles of ice solid equivalent of drizzle and resemble snow

pellets in appearance but with diameters less than 1 mm

never fall in shower fall in small quantities from stratus clouds or

from fog

HAILHAIL

►round or irregular lumps of ice round or irregular lumps of ice produced by convective clouds produced by convective clouds (cumulonimbus)(cumulonimbus)

►hail has diameter greater than 5 mmhail has diameter greater than 5 mm►can reach size of grapefruitscan reach size of grapefruits►cause significant damage to propertycause significant damage to property

Hail DamageHail Damage

How Hail FormsHow Hail Forms

► in thunderstorms that have tremendous in thunderstorms that have tremendous updrafts and down draftsupdrafts and down drafts

►hailstones begin as tiny ice crystals hailstones begin as tiny ice crystals that grow in size by accretion (adding that grow in size by accretion (adding layer after layer of ice) as they are layer after layer of ice) as they are thrown into water droplets in the stormthrown into water droplets in the storm

►storm updrafts suspend hailstones until storm updrafts suspend hailstones until they are too large and fallthey are too large and fall

Hail FormationHail Formation

Huge Hail

Hail Damage